Where is bpy.context.material?
Best guess:

You can see that bpy.context.material is listed under the "Buttons Context" section in the API doc link you posted (other sections are "View3D Context", "Screen Context" etc.). Based on what I found during my search, it looks like this is a context from 2.4x that is no longer available in 2.5x+. "Buttons Context" seems to be an old name for what we now know as the properties editor.

http://wiki.blender.org/index.php/Doc:2.4/Reference/Buttons/Window

It seems that this is old code (or old documentation) that just wasn't removed, but take it with a grain of salt, I could easily be wrong.

Edit (from comment below, which author identified as the sought-after code):
If I get what you're looking for with this attribute, you might want to try bpy.context.object.active_material.